Because factory farming isn't 'the circle of life'. It's completely separate from the actual food chain. There is nothing natural about factory farming. It would take me too long to get into every issue of factory farming, so I'll just link you to a short video that summarizes some of the standard practices in factory farming.
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I think vegetarians might be interested. I stopped eating meat about 2 years ago, but didn't know gelatin was made of bones until a year ago (because I'm goddamn retarded, apparently). It's good to know where your food comes from in any case

Lack of protein isn't really a problem, you can get protein in a whole range of foods. There's no magic vitamin in meat which you can't easily get from somewhere else. Iron is one you have to be careful with though, because most people do get that from meat unless they deliberately find substitute sources (which can be done easily, but you have to look into it for about 20 minutes)

While it is true that sacrifice is necessary for our existence to continue, the needless pain and slaughter of other creatures, both sentient and no, is not something we as society find as 'progressive', which is why we idolize such peaceful figures as Nelson Mandella, Mohandas Gandhi, Dr. Martin Luther King, Jr., and Abraham Lincoln, among others. To imply that the death of others is what brings us forward as a species seems to be against our very nature- our humanity. At least, these sentiments are what I hope that my fellow man shares and holds dear.

There is no need to eat meat or other animal products to sustain a healthy life, according to the American Dietetic Association, with a properly planned diet, thus making the death and pain of animals unnecessary.

Actually, Oreos are vegan, the filling is made of vegetable oils and soy. The sugar used in the cookie is filtered using a process that isn't vegan though. Then again I don't care because bacon is delightful.

Wanna know something funny? Ok, so you know how there are hipster vegans out there that love using ****** film cameras because they think it's cool? Well next time you meet one you can tell them that film contains a fair amount of gelatin made from animal bones and pig fats, it's used as a bonding agent for the emulsion. I think it's hilarious.
Source: I'm a photography teacher.